The University of California, San Francisco, in collaboration with Walden House, Inc., is proposing a research and demonstration project to study the efficacy of a day treatment model for the problems of substance abuse and to compare this intensive day treatment to a standard residential treatment. The comparison in substance abuse treatment, rehabilitation, and HIV-AIDS education/prevention. Day treatment has been employed extensively in mental health service delivery systems, but has not been widely applied in the field of substance abuse treatment. It has significant potentials for increasing access and decreasing costs of substance abuse treatment and rehabilitation. This project investigates the benefits of providing day treatment to drug abusers, and compares day treatment and residential treatment. The project has two phases: 1) a one-year Program Demonstration Phase, and 2) a four-year Randomized Clinical Trial. The Program Demonstration Phase will enhance and expand an existing day treatment program; define and describe the program; implement a standardized psychoeducational HIV risk-reduction intervention; establish the treatment protocol and measures for use randomized trial; estimate the effective size of comparison groups and finalize other aspects of the randomized study. The randomized clinical trial, comparing effectiveness of day treatment and residential treatment models, will be completed during project years 02 through 05. In the initial project phase, 90 clients admitted to day treatment will be recruited and assessed at baseline using a series of core measurements. In Phase Two, 150 participants in each condition will be followed up to 18 months post admission, with comparison on dimensions of treatment participation and retention, substance abuse behavior, employment status and legal involvement, and HIV risk behavior and serostatus. The long-term project goal is to demonstrate an effective innovative day treatment model to reduce problems of drug abuse and to slow the spread of HIV among intravenous drug users. The proposed study will answer questions concerning the use of drug abuse day treatment models and the comparative effectiveness of day treatment as an alternative to residential models.